The invention relates to a device, such as disclosed in European patent publication EP 0 834 968 A2, for transmitting current between two terminals, between which is arranged at least one ribbon cable that is accommodated in a cassette and extends in turns, having at least two electrical conductors the length of which is substantially greater than the distance between the two terminals. In this device, the cassette comprises a fixed stator and a rotatable rotor between which the ribbon cable is arranged. At least one of the two terminals is movable relative to the other, and the ribbon cable at its ends located in the area of the terminals is brought out of the cassette.
Such devices are used, for instance, for the power supply of an airbag in a motor vehicle. In this application, the device is built into the steering wheel of the motor vehicle. A significant problem in this and similar devices in general is the current transmission between fixed and movable parts of the device. This problem occurs in all devices with two terminals movable relative to one another, one of which is usually stationary. The sliding contacts or slip rings that are typically used in such cases are subject to wear and are disadvantageous, especially at low amperages, because of their fluctuating contact resistances.
The device known from German patent publication DE 91 07 726 U1 manages without such sliding contacts. In this device, the current is transmitted by a ribbon cable (hereinafter referred to as xe2x80x9cFL-BLxe2x80x9d for short) which is wound between the terminals in the fashion of a spring barrel of a clock. With a relative rotational movement of the terminals connected by the FL-BL, the FL-BL, which is accommodated in a cassette, xe2x80x9cbreathesxe2x80x9d like the spring of a clock. The turns of the FL-BL are tightened to a smaller diameter in the one direction of rotation. They open out to a larger diameter in the other direction of rotation. The ends of the FL-BL are bent sharply and brought out of the cassette, and serve to connect the FL-BL to a power source on the one hand and to control elements on the other hand. The mechanically sensitive conductors of the FL-BL and the bending point are mechanically protected by a protection element surrounding the ribbon cable. In this device, problems occur when the FL-BL becomes wider because of a greater number of conductors. A correspondingly longer or wider space to lead through the FL-BL surrounded by the protection element is typically not available.
In the known device disclosed in the initially mentioned EP 0 834 968 A2, the ends of the FL-BL are also sharply bent and brought out of the cassette. A protection element surrounding the FL-BL and its bending point is mounted at each end. The protection element, like the ribbon cable, is divided into at least two flat partial elements that extend parallel to one another and in the mounted state fit against one another with their flat sides. This preserves the protection element as mechanical protection of the bent part of FL-BL. To mount the cassette to or inside parts of a steering wheel of a motor vehicle, the length or width of the opening to pass through the protection element may remain unchanged. It has to be widened only slightly so that a protection element consisting of two or more partial elements can be passed through. The at least two-part protection elements are additional elements that have to be fabricated separately.
The object of the invention is further to develop the initially described device so that it is simpler to produce and mount.
According to the invention, this object is attained by an arrangement wherein
on the outside of the stator of the cassette at least two plate-shaped contact carriers are mounted, which enclose a clearance to receive mutually insulated electrical contacts to which the conductors of the FL-BL on the one hand and the conductors of at least one continuing electrical cable on the other hand can be connected, and
the contact carriers as well as any additional contact carriers are connected in piggyback fashion by elastic snap-in elements.
This device can be used largely independently of the number of conductors of the FL-BL. In the finished device, the conductors of the FL-BL are connected to the contacts of at least one contact carrier of the cassette. If, for instance, two contact carriers equipped with contacts are used, the ends of an FL-BL can be divided in accordance with the number of contacts of the two different contact carriers. It is also possible, however, to use two FL-BLs the conductors of which can be connected separately from one another with the contacts of different contact carriers. This is advantageously done at the time when the FL-BL is prepared, prior to fixing the contact carriers to the cassette. The conductors of the FL-BL (one or more than one) can be connected with the contacts of the contact carrier in an electrically conductive manner, e.g., by soldering or welding. A first contact carrier can then be connected either directly to the cassette or to a support mounted thereto. All other contact carriers can for example be snapped onto the first or onto a previously mounted contact carrier in piggyback fashion by means of elastic snap-in elements. The respective unit of contact carriers can be mounted to an end face or a circumferential surface of the cassette. Another essential advantage of this device is that basically the same structure can be used for the cassette with the contact carriers irrespective of the number of conductors of the FL-BL and the continuing cables. Only at least one each of the contact carriers has to be equipped with electrical contacts to connect the corresponding conductors. The second or the additional contact carriers need to carry contacts only if a correspondingly greater number of conductors is to be connected. Accordingly, only as many contacts-which are relatively expensive-are used in the contact carriers as are required to connect the conductors. Thus, it is also possible to build contact carriers without contacts into a unit. The external appearance of the cassette is always the same, no matter how many conductors its FL-BL has.